WO2012070349A1 - Acier non traité thermiquement pour une nitruration douce et composant nitruré par nitruration douce - Google Patents

Acier non traité thermiquement pour une nitruration douce et composant nitruré par nitruration douce Download PDF

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WO2012070349A1
WO2012070349A1 PCT/JP2011/074645 JP2011074645W WO2012070349A1 WO 2012070349 A1 WO2012070349 A1 WO 2012070349A1 JP 2011074645 W JP2011074645 W JP 2011074645W WO 2012070349 A1 WO2012070349 A1 WO 2012070349A1
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soft
soft nitriding
less
bending
steel
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PCT/JP2011/074645
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English (en)
Japanese (ja)
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成史 西谷
幹 高須賀
松本　斉
将人 祐谷
明 谷山
佐野　直幸
江頭　誠
高橋　宏昌
勇 斎藤
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住友金属工業株式会社
本田技研工業株式会社
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Priority to CN201180056073.7A priority Critical patent/CN103221566B/zh
Priority to JP2012545662A priority patent/JP5639188B2/ja
Priority to BR112013009229A priority patent/BR112013009229B1/pt
Publication of WO2012070349A1 publication Critical patent/WO2012070349A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/28—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for plain shafts
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/30—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for crankshafts; for camshafts
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium

Definitions

  • the present invention relates to a non-tempered steel for soft nitriding and a soft nitrided part.
  • soft nitriding parts parts used for soft nitriding
  • crankshafts which are engine parts for automobiles, construction machines, etc.
  • quenching-tempering after rolling.
  • the present invention relates to a soft nitriding steel (hereinafter referred to as “non-tempered steel for soft nitriding”) suitable for use as a material of the component without being subjected to heat treatment such as “normalizing”, “annealing”, or the like.
  • the present invention relates to a non-tempered steel for soft nitriding that can provide the above-mentioned characteristics to a soft-nitrided part even when water cooling is performed in a cooling step after soft nitriding.
  • Parts that require high bending fatigue strength and wear resistance such as crankshafts for automobiles and construction machinery, are in a non-tempered state after being formed into a predetermined rough shape by hot forging and machining.
  • surface hardening treatment such as induction hardening or soft nitriding is performed.
  • the soft nitriding treatment is characterized in that there is less distortion generated during the surface hardening treatment than the induction hardening treatment.
  • parts such as a crankshaft are often subjected to soft nitriding, but even in the case of soft nitriding, no distortion can be eliminated.
  • the nitrocarburized part in which strain is generated by the soft nitriding treatment is subjected to a bending correction process in a finishing process after the soft nitriding process to remove the strain.
  • the soft nitriding component whose surface layer is excessively hardened is subjected to a bending correction treatment, cracks may occur in the soft nitriding layer on the surface.
  • the bending fatigue strength that the nitrocarburized component originally had before the bending straightening process is greatly reduced.
  • the surface layer hardness of the soft nitriding component is increased, so that a reduction in bending straightness is inevitable. Therefore, the soft nitriding part is also required to have excellent bending straightness.
  • Patent Document 1 discloses “non-tempered steel for soft nitriding” and Patent Document 2 discloses “non-tempered steel for soft nitriding”.
  • Patent Document 1 in mass%, C: 0.2 to 0.6%, Si: 0.05 to 1.0%, Mn: 0.25 to 1.0%, S: 0 0.03-0.2%, Cr: 0.2% or less, s-Al: 0.045% or less, Ti: 0.002-0.010%, N: 0.005-0.025%, and O: 0.001 to 0.005% is contained, and if necessary, Pb: 0.01 to 0.40%, Ca: 0.0005 to 0.0050% and Bi: 0.005 to 0.40% And satisfying the conditions of [0.12 ⁇ Ti ⁇ O ⁇ 2.5 ⁇ Ti] and [0.04 ⁇ N ⁇ O ⁇ 0.7 ⁇ N], “Non-tempered steel for soft nitriding” is characterized in that the balance consists of Fe and inevitable impurities, and the structure after hot forging is a mixed structure of ferrite and pearlite. It is.
  • Patent Document 2 discloses a non-tempered steel having a nitrocarburized layer on the surface and a steel cross-sectional structure excluding the nitrocarburized layer having a ferrite + pearlite structure, and the composition of the steel is mainly composed of Fe.
  • C 0.30 to 0.50%
  • Si 0.05 to 0.30%
  • Mn 0.50 to 1.00%
  • S 0.03 to 0.20%
  • Cu 0.05 to 0.60%
  • Ni 0.02 to 1.00%
  • Cr 0.05 to 0.30%
  • N 0.0050 to 0.0250%
  • O 0.0005 to 0.008%
  • Ca one or both of 0.0005 to 0.0050%, Cu , Ni and Cr content ratios as WCu, WNi and WCr, respectively.
  • Patent Document 1 In the case of the technique disclosed in Patent Document 1 described above, the bending fatigue strength does not reach 600 MPa. Furthermore, Patent Document 1 does not mention any cooling method in the cooling step after soft nitriding.
  • the present invention provides a soft nitriding component that stably has a high bending fatigue strength of 600 MPa or more and an excellent bend straightening property even when subjected to water cooling in the cooling step after soft nitriding, and a material for the soft nitriding component It is an object of the present invention to provide a non-heat treated steel suitable for soft nitriding.
  • (A) Mn is an element that can provide a high bending fatigue strength to a soft-nitrided component at low cost without containing expensive alloy elements such as Mo and V.
  • (C) Cr is contained as an impurity in steel, and its content greatly affects the bending fatigue strength and bend straightening properties of nitrocarburized parts.
  • the diffusion layer depth can be increased without excessively hardening the surface layer of the soft nitrided component. Thereby, it is possible to provide the soft nitriding part with high bending fatigue strength and excellent bending straightening property.
  • Mn not only strengthens the surface layer by increasing the dissolved nitrogen, but also strengthens the surface layer by forming fine Mn nitride. Specifically, when soft nitriding is performed using a non-tempered steel with an increased Mn content, a plate-like fine ⁇ -Mn 3 N 2 having a thickness of 5 nm or less and a width of 200 nm or less is obtained. It precipitates while maintaining a consistent state in the ferrite of the mixed structure of ferrite and pearlite constituting the diffusion layer (hereinafter referred to as “ferrite / pearlite structure”).
  • the fine plate-like precipitates that are coherently precipitated in the ferrite as a material improve the strength of the soft nitrided part and contribute to the improvement of bending fatigue strength. And since the precipitation of this fine plate-like precipitate is almost completed while being kept at the high temperature during soft nitriding, the influence of the cooling rate in the cooling step after soft nitriding is small. Therefore, even if water cooling treatment is performed in the cooling step after soft nitriding, the soft nitriding component can be stably provided with high bending fatigue strength and excellent bend straightening.
  • the present invention has been completed based on the above findings, and the gist of the present invention resides in the non-heat treated steel for soft nitriding shown in the following (1) and the soft nitriding component shown in (2).
  • the chemical composition of the dough is mass%, C: 0.25% or more and less than 0.35%, Si: 0.15 to 0.35%, Mn: 0.85 to 1.20%, S : 0.10% or less, Al: more than 0.010% and 0.030% or less, Ti: 0.003-0.020% and N: 0.010-0.024%, the balance being Fe And P and Cr in the impurity are P: 0.08% or less and Cr: 0.10% or less, respectively, and P1 represented by the following formulas (1) and (2): P2 is P1 ⁇ 0.96 and P2 ⁇ 0.90, respectively,
  • the diffusion layer has a ferrite / pearlite structure, and the number of plate-like precipitates having a thickness of 5 nm or less and a width of 200 nm or less deposited in the ferrite is 130 to 250 / ⁇ m 2 .
  • the “impurities” in the “Fe and impurities” as the balance refers to those mixed from the ore, scrap, or production environment as raw materials when industrially producing steel materials.
  • the soft nitriding component of the present invention stably has a high bending fatigue strength of 600 MPa or more and excellent bend straightening properties even when subjected to water cooling in various soft nitriding conditions, particularly in the cooling step after soft nitriding. It is suitable as a crankshaft. If the non-tempered steel for soft nitriding of the present invention is used as a raw material, the soft nitrided part can be easily manufactured.
  • FIG. 1 It is a figure which illustrates typically the method of cutting out the sample for transmission electron microscope observation from the 4-point bending test piece of the shape shown in FIG. Is a diagram showing an example of a bright-field image when the internal ferrite was observed by a transmission electron microscope in the ferrite-pearlite structure of the soft-nitriding after the diffusion layer, those shown by the white arrow in FIG, eta-Mn 3 N 2 .
  • g ( 020) Excited and observed systematic reflection of ⁇ -Fe .
  • the black arrow in the figure indicates the direction of the excited system reflection g vector in the reciprocal space.
  • the spot shape in the figure is the ⁇ -Fe diffraction pattern, and the one extending vertically and horizontally in a streak pattern is the ⁇ -Mn 3 N 2 diffraction pattern.
  • the fact that a diffraction pattern extending in a streak shape is obtained is unique to thin plate-like precipitates.
  • C Chemical composition of unrefined steel for soft nitriding and base material of soft nitriding part: C: 0.25% or more and less than 0.35%
  • C is an element effective for ensuring the bending fatigue strength after soft nitriding, and the strength of the fabric required to obtain a high bending fatigue strength of 600 MPa or more.
  • it is necessary to make it content of 0.25% or more.
  • the content of C becomes excessive, the surface hardness becomes excessively high. Furthermore, the area fraction of ferrite becomes low, and the ferrite / pearlite structure becomes coarse. For this reason, sufficient bending correction property cannot be obtained. Therefore, the C content is 0.25% or more and less than 0.35%.
  • Si 0.15-0.35%
  • Si is an element necessary for deoxidation at the time of melting, and in order to obtain this effect, the content needs to be at least 0.15%. However, since a large amount of Si causes an excessive decrease in the bending straightness, the Si content is set to 0.15 to 0.35%.
  • the Si content is preferably 0.15% or more, and preferably 0.30% or less.
  • Mn 0.85 to 1.20%
  • Mn is an element effective for deoxidation of steel, like Si.
  • Mn increases the amount of dissolved nitrogen in the nitrocarburized layer during soft nitriding, further forms intruded nitrogen and fine plate-like Mn nitride, and the nitride precipitates in the material to bend. Improve fatigue strength.
  • the Mn content needs to be 0.85% or more.
  • the Mn content is set to 0.85 to 1.20%.
  • the Mn content is preferably 0.90% or more.
  • S 0.10% or less S is contained as an impurity. Moreover, if it adds, it has the effect
  • the S content is preferably 0.08% or less. In order to obtain the machinability improving effect, the S content is preferably 0.04% or more.
  • Al more than 0.010% and 0.030% or less Al is an element effective for increasing the diffusion layer depth during soft nitriding and improving the bending fatigue strength. In order to obtain this effect, an Al content exceeding 0.010% is required. However, when the Al content is excessive, the surface hardness becomes excessively high, so that the bend straightening property is lowered. For this reason, the content of Al exceeds 0.010% and is set to 0.030% or less.
  • Ti 0.003-0.020%
  • Ti is an element that suppresses coarsening of crystal grains, refines crystal grains, and improves bending fatigue strength. In order to obtain such an effect, a Ti content of 0.003% or more is necessary. However, when the Ti content exceeds 0.020%, the bend straightening property is lowered. Therefore, the Ti content is set to 0.003 to 0.020%.
  • the Ti content is preferably 0.005% or more, and preferably 0.015% or less.
  • N 0.010 to 0.024%
  • N is an element that improves the bending fatigue strength and the bending straightness. In order to obtain such an effect, an N content of 0.010% or more is necessary. On the other hand, the above effect is saturated even if N is contained in excess of 0.024%. Therefore, the N content is set to 0.010 to 0.024%.
  • the N content is preferably 0.012% or more, and preferably 0.022% or less.
  • impurities refer to those mixed from ore, scrap, or the production environment as raw materials when industrially producing steel materials.
  • P 0.08% or less
  • P is an impurity and is an undesirable element that reduces the bending fatigue strength.
  • the content of P in the impurities is set to 0.08% or less.
  • the content of P in the impurities is preferably 0.03% or less.
  • Cr 0.10% or less Cr is contained in steel as an impurity, and its content greatly affects the bending fatigue strength and the bending straightness. In particular, when the Cr content exceeds 0.10%, the bending straightness is remarkably deteriorated. Therefore, the content of Cr in the impurities is set to 0.10% or less.
  • P1 0.96 or more
  • P1 expressed by (1) needs to satisfy P1 ⁇ 0.96.
  • C, Mn, Cr and Al in the above formula (1) mean the content of the element in mass%.
  • the bending fatigue strength can be arranged by the above P1. And when P1 is 0.96 or more, a bending fatigue strength of 600 MPa or more is obtained. This will be described below.
  • the above steel was forged into a steel bar having a diameter of 90 mm, and further forged into a steel bar having a diameter of 50 mm under the conditions of a heating temperature of 1200 ° C. and a finishing temperature of 1000 to 1050 ° C. After forging, it was allowed to cool in the air and cooled to room temperature.
  • Table 1 also shows the above Ono-type rotary bending fatigue test results.
  • FIG. 2 shows the relationship between P1 and bending fatigue strength.
  • P1 is the content of the element defined by the formula (1), 1 when C is close to 0.35%, Mn is 1.20%, Cr is 0.10% and Al is 0.030%. It may be a value close to .10.
  • P2 0.90 or more
  • C, Mn, Cr and Al in the above formula (2) mean the content in mass% of the element.
  • the bending straightness can be arranged by the above P2. And when P2 is 0.90 or more, good bend straightening is obtained. This will be described below.
  • the above steel was forged into a steel bar having a diameter of 90 mm, and further forged into a steel bar having a diameter of 50 mm under the conditions of a heating temperature of 1200 ° C. and a finishing temperature of 1000 to 1050 ° C. After forging, it was allowed to cool in the air and cooled to room temperature.
  • a 2 mm strain gauge was bonded to the notch bottom of the 4-point bending test piece obtained as described above, and bending correction strain was applied until the strain gauge was disconnected.
  • the strain gauge adhered to the surface layer is disconnected, so the bending straightness was evaluated by the amount of strain at the time when the strain gauge was disconnected, that is, the amount of bending correctable strain.
  • Each of the four-point bending test pieces in which the strain gauge is disconnected is embedded in the resin so that the R3 notch bottom vertical section of the four-point bending test piece is the test surface, and then the surface is mirror-finished. It was confirmed that there was a crack in the soft nitrided layer using an optical microscope.
  • the target for bending straightening property was that the above-mentioned bending straightening possible strain amount was 20000 ⁇ or more.
  • Table 2 also shows the amount of strain that can be straightened, which is an index of the above straightening properties.
  • FIG. 4 shows the relationship between P2 and the amount of distortion that can be corrected.
  • P2 is the value of the element defined by the formula (2), C is close to 0.35%, Mn is 0.85%, Cr is close to 0%, and Al is close to 0.010%. A value close to 1.97 in the case of.
  • the non-tempered steel for soft nitriding of the present invention having the above-described chemical composition is forged under normal hot forging conditions, for example, a heating temperature of 1200 to 1300 ° C. and a finishing temperature of 900 to 1100 ° C. If it is allowed to cool in the air and then cooled to room temperature, a non-heat treated steel material having a ferrite-pearlite structure in which the area fraction of ferrite is 30 to 80% and the balance is pearlite can be obtained.
  • the soft nitriding component of the present invention is obtained by forming the above-mentioned non-tempered steel material into a part shape by machining, and then performing a soft nitriding treatment under conditions of a soaking temperature of 450 to 650 ° C. and a soaking time of 30 minutes or more. can get. Soaking temperature of above is sufficiently lower than the A 3 transformation point of steel, cloth and the diffusion layer of the non-heat treated steel is not able to phase transformation during the nitrocarburizing treatment, nitrocarburizing components tissues soft It has the same ferrite-pearlite structure as the non-tempered steel before nitriding. Therefore, the diffusion layer of the soft nitrided component of the present invention is composed of a ferrite pearlite structure.
  • the soft nitrided part of the present invention has 130 to 250 / ⁇ m 2 of plate-like precipitates having a thickness of 5 nm or less and a width of 200 nm or less in the ferrite in the ferrite / pearlite structure of the diffusion layer. is there. If the above plate-like precipitate is present in the ferrite, the soft-nitriding component should have a high bending fatigue strength of 600 MPa or more and a target bending straightness of 20000 ⁇ or more in terms of the amount of bend straightening. Because you can.
  • a compound that is finely and consistently precipitated with respect to the dough improves the strength of the dough as a precipitation strengthening factor, and the greater the amount of precipitation and the smaller the size, the greater the contribution to precipitation strengthening.
  • precipitates having a large size such that at least one of thickness and width exceeds the above values hardly contributes to strengthening of the soft nitrided component of the present invention.
  • the thickness and width of the plate-like precipitates present in the ferrite are preferably 3 nm or less and 100 nm or less, respectively.
  • an observation device such as a transmission electron microscope (hereinafter referred to as “TEM”), when TEM observation is performed at a magnification of 200000 times, a precipitate having a thickness of 1 nm and a width of 10 nm becomes an observation limit.
  • TEM transmission electron microscope
  • the diffusion layer of the nitrocarburized part described in the section (B) is made of steel having the chemical composition described in the section (A), under a condition of a soaking temperature of 450 to 650 ° C. and a soaking time of 30 minutes or more. It can be obtained by performing a soft nitriding treatment.
  • steel having the chemical composition described in the above section (A) is used, the influence of the cooling rate after the soft nitriding treatment on the component characteristics is not excessively large, and any cooling method is adopted. Satisfy the goal. For this reason, the cooling after soft nitriding may be performed by an appropriate method.
  • Steels A to E in Table 3 are steels whose chemical compositions are within the range specified by the present invention.
  • steels F to N are steels whose chemical compositions deviate from the conditions defined in the present invention.
  • the above steel was forged into a steel bar having a diameter of 90 mm, and further forged into a steel bar having a diameter of 50 mm under the conditions of a heating temperature of 1200 ° C. and a finishing temperature of 1000 to 1050 ° C. After forging, it was allowed to cool in the air and cooled to room temperature.
  • the R3 groove bottom longitudinal section of the four-point bending test piece was embedded in a resin so as to be a test surface, mirror-polished, and then corroded with nital to reveal the structure. Thereafter, a five-field observation of a portion at a depth of 1 mm from the surface layer was performed with an optical microscope at a magnification of 100 times to identify a phase, and an area fraction (%) of ferrite was measured.
  • Steel C and steel D were soft-nitrided even under conditions of a soaking temperature of 650 ° C. and a soaking time of 180 minutes. After soft nitriding, all were water-cooled.
  • the diffusion layer was investigated using a four-point bending test piece that was water-cooled after the soft nitriding treatment. Specifically, it was embedded in a resin so that the R3 groove bottom longitudinal section of the four-point bending test piece was a test surface, mirror-polished, then corroded and washed with nital. Thereafter, five consecutive positions from the surface layer to a depth of 1 mm are observed with an optical microscope at a magnification of 100 times, and an uncorroded portion near the surface, that is, the depth of the compound layer formed on the surface layer. In addition, the phases in the corroded region deeper than the compound layer were identified.
  • Vickers hardness at consecutive positions from 0.05 mm to 1 mm in depth at any three locations is measured according to “Vickers hardness test-test method” described in JIS Z 2244 (2009). Then, the value of the same depth was averaged to create a hardness transition curve as the hardness distribution, and the depth of the nitride layer, which is the sum of the depths of the compound layer and the diffusion layer, was investigated.
  • the measurement of Vickers hardness was performed under the conditions of a test force of 2.94 N and a measurement interval in the depth direction of 0.05 mm.
  • the definition of the nitrided layer conforms to JIS G 0562 (1993), and the nitrided layer depth refers to the distance from the surface until the difference in hardness cannot be distinguished from the fabric.
  • the nitrided layer depth was found to be 0.55 to 0.80 mm. Therefore, the internal structure of the diffusion layer was further investigated for the four-point bending test piece that was water-cooled after the soft nitriding treatment. Specifically, as shown in FIG. 5, a plate-shaped test piece having a thickness of 1 mm including the surface of the smooth portion was cut out from the four-point bending test piece. Next, the plate-like test piece having a thickness of 1 mm is mechanically polished from both sides so that the thickness decreases in the depth direction from the surface of the smooth portion, and includes only the position of 30 to 90 ⁇ m in depth from the surface of the smooth portion. It processed into the plate-shaped test piece.
  • the plate-like test piece was further thinned by twin-jet electrolytic polishing using a perchloric acid-methanol mixture, and energy dispersive X-ray spectroscopy (STEM-EDS) using a scanning transmission electron microscope. )
  • STEM-EDS energy dispersive X-ray spectroscopy
  • the acceleration voltage in STEM-EDS analysis and TEM observation is 300 kV.
  • the ferrite portion in the ferrite / pearlite structure could be observed by TEM. Therefore, since it was confirmed that the above-mentioned thin film test piece was taken from the diffusion layer, not the compound layer, the characteristics of the precipitate shape and the precipitation form were investigated by TEM observation, and STEM-EDS Thus, the elements constituting the precipitate were investigated.
  • FIG. 6 is a bright field image
  • FIG. 7 is an electron diffraction pattern of the same field.
  • the precipitate is ⁇ -Mn 3 N 2 and has a plate-like shape in which the orientation relationship with the ferrite material is [Equation 1] and [Equation 2]. found.
  • the ⁇ -Mn 3 N 2 deposited so as to satisfy [Equation 3] or [Equation 4] is observed so that the plate is viewed from the horizontal direction when the electron beam incident direction is [001] ⁇ -Fe. Therefore, it is observed as a linear contrast as in the observation example.
  • the thickness of the linear precipitate is defined as the thickness of the plate-like precipitate and the length is defined as the width
  • ⁇ -Mn 3 N 2 having a thickness of 1 nm and a width of 10 nm is observed. It was the limit.
  • a 2 mm strain gauge was bonded to the notch bottom of a four-point bending test piece that was water-cooled after soft nitriding, and bending correction strain was applied until the strain gauge was disconnected.
  • the bend straightness was evaluated by the amount of strain at the time when the strain gauge was disconnected, that is, the amount of bending correctable strain.
  • the target of the amount of strain that can be straightened as an index of the straightening property is 20000 ⁇ or more.
  • Test Nos. 1 to 7 according to “Examples of the present invention” satisfying the conditions defined in the present invention achieved the goals of a bending fatigue strength of 600 MPa or more and a bending correctable strain amount of 20000 ⁇ or more, which are high. It is clear that in addition to bending fatigue strength, it has excellent bend straightening properties.
  • the test No. 8 has a low C content of steel F as low as 0.20%, which is outside the conditions defined in the present invention.
  • the number of plate-like nitrides having a thickness of 5 nm or less and a width of 200 nm or less precipitated in the ferrite of the diffusion layer is 176 / ⁇ m 2 , which satisfies the provisions of the present invention, but the strength of the dough is insufficient.
  • the bending fatigue strength as a soft nitrided part did not reach the target.
  • the Mn content of Steel G is as low as 0.80%, which is outside the conditions defined in the present invention.
  • the number of plate-like precipitates having a thickness of 5 nm or less and a width of 200 nm or less deposited in the ferrite of the diffusion layer is as small as 112 / ⁇ m 2 , which is outside the conditions defined in the present invention. For this reason, the bending fatigue strength as a soft nitriding component has not reached the target.
  • Test number 10 has a low Al content of steel H as low as 0.003%, which is outside the conditions defined in the present invention. For this reason, the diffusion layer depth did not increase during soft nitriding, and the bending fatigue strength as a soft nitriding component did not reach the target.
  • Test No. 11 has a parameter P1 of steel I of 0.95, which is lower than the range specified in the present invention. For this reason, the bending fatigue strength as a soft nitriding component has not reached the target.
  • the Mn content of Steel J is as high as 1.25%, which is out of the conditions defined in the present invention.
  • the number of plate-like precipitates having a thickness of 5 nm or less and a width of 200 nm or less deposited in the ferrite of the diffusion layer is as large as 257 / ⁇ m 2 , which is outside the conditions defined in the present invention. For this reason, the amount of strain that can be bent as a soft-nitrided part has not reached the target, and the bending straightness is poor.
  • Test No. 13 has a high Cr content of steel K of 0.11%, which is out of the conditions defined in the present invention. For this reason, the amount of strain that can be bent as a soft-nitrided part has not reached the target, and the bending straightness is poor.
  • Test number 14 has a high Al content of steel L as high as 0.060%, which is outside the conditions defined in the present invention. For this reason, the amount of strain that can be bent as a soft-nitrided part has not reached the target, and the bending straightness is poor.
  • Test number 15 is lower than the range defined in the present invention, with the parameter P2 of steel M being 0.89. For this reason, the amount of strain that can be bent as a soft-nitrided part has not reached the target, and the bending straightness is poor.
  • Test No. 16 has a high C content of steel N of 0.42%, which is outside the conditions defined in the present invention. For this reason, the amount of strain that can be bent as a soft-nitrided part has not reached the target, and the bending straightness is poor.
  • the soft nitriding component of the present invention stably has a high bending fatigue strength of 600 MPa or more and excellent bend straightening properties even when subjected to water cooling in various soft nitriding conditions, particularly in the cooling step after soft nitriding. It is suitable as a crankshaft. If the non-tempered steel for soft nitriding of the present invention is used as a raw material, the soft nitrided part can be easily manufactured.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

La présente invention concerne : un composant nitruré par nitruration douce qui, même lorsqu'il a été produit par un refroidissement à l'eau après une nitruration douce, a une résistance à la fatigue de souplesse de 600 MPa ou plus et une excellente aptitude au redressage ; et un acier non traité thermiquement pour une nitruration douce, qui est approprié pour une utilisation en tant que matière première pour le composant nitruré par nitruration douce. L'acier non traité thermiquement pour une nitruration douce a une composition chimique qui contient 0,25-0,35 %, en excluant 0,35 %, de C, 0,15-0,35 % de Si, 0,85-1,20 % de Mn, jusqu'à 0,10 % de S, 0,010-0,030 %, en excluant 0,010 %, d'Al, 0,003-0,020 % de Ti et 0,010-0,020 % de N, le reste étant composé de Fe et des impuretés, dans lequel P≤0,08 % et Cr ≤0,10 % et qui satisfait 0,02C+0,22Mn+0,87Cr+0,85Al+0,72≥0,96 et 2,40C-0,54Mn-9,26Cr-0,01Al+1,59≥0,90.
PCT/JP2011/074645 2010-11-22 2011-10-26 Acier non traité thermiquement pour une nitruration douce et composant nitruré par nitruration douce WO2012070349A1 (fr)

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CN201180056073.7A CN103221566B (zh) 2010-11-22 2011-10-26 软氮化用非调质钢以及软氮化部件
JP2012545662A JP5639188B2 (ja) 2010-11-22 2011-10-26 軟窒化用非調質鋼および軟窒化部品
BR112013009229A BR112013009229B1 (pt) 2010-11-22 2011-10-26 aço não tratado termicamente para nitrocarbonetação e componente nitrocarbonetado

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WO2015190618A1 (fr) * 2014-06-13 2015-12-17 新日鐵住金株式会社 Tôle d'acier de nitruration douce, son procédé de fabrication et acier nitruré par nitruration douce
WO2018117015A1 (fr) * 2016-12-22 2018-06-28 新日鐵住金株式会社 Acier raffiné non thermique pour nitrocarburation, pièce nitrocarburée et procédé de fabrication de pièce nitrocarburée
US11274354B2 (en) 2016-04-05 2022-03-15 Daido Steel Co., Ltd. Steel material, crankshaft, and automobile component

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CN103789660B (zh) * 2014-01-21 2016-07-13 广西柳工机械股份有限公司 非调质铰接销轴及其制造方法
CN109983326A (zh) * 2016-11-09 2019-07-05 Imec 非营利协会 用于组合的stem和eds断层摄影的装备
CN112442641A (zh) * 2019-08-29 2021-03-05 广州汽车集团股份有限公司 一种发动机高强度曲轴及其制备方法

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WO2015190618A1 (fr) * 2014-06-13 2015-12-17 新日鐵住金株式会社 Tôle d'acier de nitruration douce, son procédé de fabrication et acier nitruré par nitruration douce
JPWO2015190618A1 (ja) * 2014-06-13 2017-04-20 新日鐵住金株式会社 軟窒化処理用鋼板およびその製造方法と軟窒化処理鋼
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US11274354B2 (en) 2016-04-05 2022-03-15 Daido Steel Co., Ltd. Steel material, crankshaft, and automobile component
WO2018117015A1 (fr) * 2016-12-22 2018-06-28 新日鐵住金株式会社 Acier raffiné non thermique pour nitrocarburation, pièce nitrocarburée et procédé de fabrication de pièce nitrocarburée
JPWO2018117015A1 (ja) * 2016-12-22 2018-12-20 新日鐵住金株式会社 軟窒化用非調質鋼、軟窒化部品、及び、軟窒化部品の製造方法

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JPWO2012070349A1 (ja) 2014-05-19
JP5639188B2 (ja) 2014-12-10

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